This invention relates generally to knee braces and more particularly to a single jointed knee brace providing supported movement about the true flexion/extension axis.
The human knee joint is one of the most stressed joints of the human body. In normal activities such as walking, running, kneeling, and climbing stairs, the load put on the knee joint can easily exceed five times the weight of the body, and for those who engage in more strenuous activities, can be much higher. Those who have experienced knee trauma are often treated by relieving pressure from the knee joint using a knee brace. Knee braces are sometimes used for short periods of time during which recovery is expected and sometimes for extended periods of time, for example, when chronic knee problems exist.
Typically, a knee brace comprises a strut for fastening to the thigh, a strut for fastening to the lower leg and a hinge axis positioned therebetween so as to reinforce a knee and to limit the range of movement. Many straps, cuffs or other securing systems for securing the knee brace to the leg are described and illustrated in the prior art.
However, regardless of the type of knee brace design, the medical community and designers of knee prosthetic and orthotic devices have long believed that the movement of the knee joint in flexion and extension does not take place in a simple hinge-like manner. Rather, it has heretofore been universally accepted that flexion and extension knee movement includes displacement and rotation, so that the same parts of a first articulating surface (the condyles of the femur) are not always in contact with the same part of a second corresponding articulating surface (the tibial plateau) with the axis of motion not being fixed. Thus, it has been believed that the knee acts not as a simple hinge joint, but turns in extension and flexion through an infinite succession of uniquely placed centres of rotation, each centre acting at a particular relative orientation of the femur and the tibia. As such, knee orthoses are provided with means for allowing the knee to rotate about the axes of rotation previously thought to exist. Some methods of accommodating the varying axes of flexion and extension include providing the joint with some lateral movement and providing complex hinge mechanisms for a knee brace.
As disclosed in U.S. Pat. No. 5,133,758 issued in 1992, Hollister has shown that the knee has a fixed flexion/extension axis through all degrees of flexion and extension movement of the knee. The fixed flexion/extension axis is directed inferiorly and posteriorly from the medial condyle portion to the lateral condyle portion and is offset from both the transverse and coronal planes equally by approximately 3.0 to 3.8 degrees.
Knee braces, however, continue to be flawed by trying to provide flexion/extension about varying axes of the previous model.
Two distinct forms of knee brace are commonly used: light support braces, providing support only to the outside of the knee, having small size, low weight, and low strength, and heavier weight bearing knee braces having more bulk, more weight, and greater strength. The required support and strength dictate the required brace. The constant force of conflicting brace hinged axis against the true flexion/extension axis increases the strength needed in prior art braces to provide stable support.
Some knee braces include compound hinges to accommodate the believed varying axes. Such compound hinges include two or more pivot points closely spaced along the natural joint defined by the knee. Examples of such compound hinges include Lerman U.S. Pat. No. 4,372,298; Marquette U.S. Pat. No. 4,793,333; Kausek et al. U.S. Pat. No. 4,732,143; and European Patent Application 0173161 in the name of Townsend.
Additional complex pivotal motion is introduced as disclosed in U.S. Pat. Nos. 5,586,970 issued to Morris, and U.S. Pat. No. RE 34818 issued to Daneman, which include additional pivotal motion of pads within the brace structure.
Many braces rely on a simple hinge axis rigidly braced with respect to the knee. Examples of such devices include Ford U.S. Pat. No. 4,624,247; Martin et al. U.S. Pat. No. 4,503,846 and Myers et al. U.S. Pat. No. 4,802,466. However, without providing hinged movement about the true flexion/extension axis there is a tendency for some knee braces to xe2x80x9cpistonxe2x80x9d with respect to the leg. The brace slides up and down the upper portion of the leg, causing irritation and discomfort. Such piston movement can be accommodated by various springs or telescoping linkages between the respective knee brace portions. Illustrative of such arrangements are British Patent Application 2,156,221 in the name of Carsalade, and U.S. Pat. No. 5,352,190 in the name of Fischer.
Unfortunately, the more supportive weight bearing knee braces which include a hinge and supporting struts on the medial and lateral sides of the knee, often have the following shortcomings: they are bulky, difficult to install or xe2x80x9cput on,xe2x80x9d heavy and less comfortable than similar single hinged knee braces. In many cases, such a brace causes damage to clothing, fatigue, difficulty in walking with a normal gait, and generally restricted mobility. Further, compound joint knee braces are difficult to adjust in order to increase comfort and orthopedic value.
The use of light support single hinge knee braces is also known. Most single hinge knee braces are designed for portability and more specifically, for lightweight applications. Essentially, the amount of support provided by single hinge knee braces is often quite limited as the brace is easily deformed.
In an attempt to overcome these and other limitations of the prior art, it is an object of the present invention to provide a single joint knee brace that provides increased strength and support while retaining many of the advantages inherent in single joint braces.
It is a further object to provide a knee brace that is comfortable and that rotates about a natural axis of rotation of the knee.
It has been found that by providing a brace structure which permits flexion/extension at the true flexion/extension axis, weight bearing support can be provided to the knee with a lighter more comfortable single hinge brace.
In accordance with the invention there is provided a single joint, weight bearing knee brace having a fixed flexion-extension axis of rotation comprising:
an upper portion for mounting to a portion of a leg above the knee;
a lower portion for mounting to a portion of a leg below the knee;
a single joint hingedly connecting the upper portion and the lower portion and having a substantially fixed flexion-extension axis,
said single joint comprising:
a first portion and a second portion interconnected for rotational movement about a hinge axis, the first portion and the second portion including interconnecting elements for securing the joint and for supporting rotational movement about the hinge axis, the interconnecting elements comprising a projecting cylindrical element having a cylindrical sleeve bearing surface for securing the joint and for supporting sliding rotational movement about the hinge axis and a cylindrical opening having a cylindrical sleeve bearing surface for receiving the projecting cylindrical element;
the first portion and the second portion further including cooperating sleeve bearing surfaces angularly disposed to the hinge axis for supporting sliding rotational movement about the hinge axis and for receiving forces in any of three dimensions and moments about any two of three coordinates having a different orientation than the hinge axis;
at least one of the first portion and the second portion further including mounting means for maintaining the fixed flexion-extension axis between 2.5 to 4 degrees posterior to the coronal plane from the medial condyle portion to the lateral condyle portion, to position the fixed flexion-extension axis approximately coaxial with the fixed flexion-extension axis of the knee.
In accordance with another aspect of the invention there is provided A brace for securing to a human leg at an upper leg above a knee and a lower leg below the knee, for supporting the knee for flexion and extension movement about a fixed flexion/extension axis oriented posteriorly and inferiorly from a medial condyle portion to a lateral condyle portion between 2.5 to 4 degrees from both the transverse and coronal planes, the brace comprising:
a single joint having an inner portion and an outer portion interconnected for rotation about a hinge axis, the inner and outer portions each including an extension arm, at least one extension arm positioned at an angle to a rotational plane perpendicular to the axis, each inner and outer portion further including interconnecting elements for securing the joint and for supporting rotational movement about the hinge axis and cooperating sleeve bearing surfaces angularly disposed to the hinge axis for supporting sliding rotational movement about the hinge axis and for receiving forces in any of three dimensions and moments about any two of three coordinates having a different orientation than the hinge axis;
a substantially rigid upper strut secured to the extension arm of the outer portion for receiving forces and moments in any of three dimensions and for transmitting the same to the outer portion;
a substantially rigid lower strut secured to the extension arm of the inner portion for receiving forces and moments in any of three dimensions from the inner portion and for transmitting the same;
an upper cuff, shaped to match the contour of a sufficiently large surface portion of the upper leg substantially exactly, for securing the upper strut in a unique position adjacent a lateral surface of the upper leg substantially aligned with the femur bone of the upper leg such that the hinge axis substantially coincides with the fixed flexion/extension axis of the knee and for transmitting forces and moments in any of three dimensions from the upper leg to the upper strut; and,
a lower cuff, shaped to match the contour of a sufficiently large surface portion of the lower leg substantially exactly, for securing the lower strut in a unique position adjacent a lateral surface of the lower leg substantially aligned with the tibia bone of the lower leg such that the hinge axis substantially coincides with the fixed flexion/extension axis of the knee and for transmitting forces and moments in any of three dimensions from the lower strut to the lower leg.
Advantageously, the present invention provides a brace offering weight bearing support which is smaller and more convenient and comfortable to wear.
Conveniently the hinge in accordance with the present invention is quite flat, while providing rigid and strong three dimensional weight bearing functionality.
Additional advantages of the present invention include mechanical simplicity, reduced cost of manufacture, and improved reliability.